WASHINGTON — With the economy in a downward spiral, U.S. troops in Iraq and Afghanistan and the nation under threat from terrorists, President Bush pledged Saturday to make a smooth transition to an Obama administration a top priority for the rest of his days in office.

"Our country faces economic challenges that will not pause to let a new president settle in," Bush said in his weekly radio address. "This will also be America's first wartime presidential transition in four decades. We're in a struggle against violent extremists determined to attack us — and they would like nothing more than to exploit this period of change to harm the American people."

In the Democrats' radio address, President-elect Obama stressed the nation must act swiftly to deal with continuing job losses and a financial meltdown that poses the "greatest economic challenge of our lifetime." He noted that he was already meeting with economic advisers.

"While we must recognize that we only have one president at a time and that President Bush is the leader of our government, I want to ensure that we hit the ground running on Jan. 20 because we don't have a moment to lose," Obama said.

Obama underscored many of the economic talking points from his news conference Friday, the first held since his victory. He said his administration's focus will be on creating jobs, stabilizing the financial markets while helping homeowners, and growing the middle class and strengthening the economy in the long-term.

"I do not underestimate the enormity of the task that lies ahead," Obama said. "We've taken some major actions to date, and we will need further actions during this transition and subsequent months. Some of those choices will be difficult, but America is a strong and resilient country."

Bush said the White House and federal agencies have been working for more than a year to make sure the next administration can get off to a quick start.

Intelligence officials have briefed Obama, the Justice Department has approved security clearances for members of his transition staff and, in the coming weeks, administration officials will brief the Obama team on major policy issues, including the Iraq war and the ailing financial markets. The president said he also would keep Obama fully informed on any important decisions he makes between now and when Obama takes over on Jan. 20.

Until then, Bush said he will continue to address the nation's economic problems and urge Congress to approve free-trade deals with Colombia, Panama and South Korea and will host an international economic summit in Washington on Nov. 15 to address the global financial crisis.

"Earlier this week, more than 120 million Americans went to the polls and voted for a new president and Congress," Bush said of the election in which Democrats gained seats in both the House and Senate. "No matter how we cast our ballots, all Americans have reason to be proud of our democracy."

Bush and first lady Laura Bush have invited Obama and his wife, Michelle, to the White House on Monday.

"I join the American people in wishing President-elect Obama every success," he said. "Laura and I wish the Obama family as much joy and happiness as our family has found in this wonderful house."

Obama said he and Michelle looked forward to the meeting.

"We can't afford to wait on moving forward on the key priorities that I identified during the campaign, including clean energy, health care, education and tax relief for middle class families," Obama said.

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